1. Field of the Invention
The present invention relates to a valve system, and more particularly to a hydraulic pressure control apparatus of a variable valve system.
2. Description of Related Art
Generally, technical investigations have been undertaken in a variety of fields of the vehicle industry. Among them, the technical field for improving fuel efficiency of an engine is very important in energy saving and environmental aspects.
An engine that has a cylinder deactivation function (CDA) deactivates a combustion chamber in an idle state or low load driving condition such that fuel efficiency is improved.
FIG. 1 is a partial perspective view of a general variable valve system, and FIG. 2 is a schematic diagram showing a hydraulic pressure control circuit of a general variable valve system.
As shown, the valve system is equipped with a variable tappet (a switchable tappet). The variable tappet is mounted on an upper end portion of a valve stem 1a. 
The variable tappet includes an inner tappet 3, an outer tappet 5 supported by a spring 1b, and a locking pin 7. And, a first cam 13 and a second cam 11 are formed on a camshaft 9.
The first cam 13 corresponds to the outer tappet 5, and the second cam 11 corresponds to the inner tappet 3. When the inner tappet 3 and the outer tappet 5 are engaged, the valve performs a high lift, and when the inner tappet 3 and the outer tappet 5 are not engaged, the valve performs a low lift, according to a position of the locking pin 7 that is moved by hydraulic pressure.
Referring to FIG. 2, variable tappets 105a and 105b are respectively disposed at an intake side and an exhaust side of a first cylinder (cyl. 1), and variable tappets 110a and 110b are respectively disposed at an intake side and an exhaust side of a fourth cylinder (cyl. 4).
Hydraulic pressure lines 120a and 120b are respectively disposed corresponding to the intake side and the exhaust side, and oil control valves (OCV) 100a and 100b are disposed in the respective hydraulic pressure lines 120a and 120b. The oil control valves 100a and 100b simultaneously supply the hydraulic pressure to the two cylinders (cyl. 1 and 4) such that the hydraulic pressure cannot be transferred with optimum timing.
Also, the oil control valves 100a and 100b are operated by an electrical system such that there is a high probability in that the oil control valves may malfunction. In addition, the oil control valves 100a and 100b increase manufacturing cost.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.